Transmission measuring means and method



April 27, 1954 w. L. BRUNE TRANSMISSION MEASURING MEANS AND METHOD FiledSept. 30. 1952 v Sheets-Sheet 1 S U 2 MR mmm Ma 3 A e Vi 1:]. 2 m

APPARA TUS UNDER TEST wve/v TOR W L. BRUNE ATTORNEY P 27, 1954 w. L.BRUNE 2,677,101

TRANSMISSION MEASURING MEANS AND METHOD Filed Sept. 30, 1952 7Sheets-Sheet 2 i VOLTAGE RAT/O F/G.5 4 c C V E A C Fla. 6

PARALLEL COMB/M47700 APPAR' OF SOURCE ATUS DETECTOR AND UNDER N0.2DETECTOR ATU I u/vom 0F 29$ L 5 TEST ASSOC/ATEO DEI'ECTOR /vo./ M

,0 CURRENT RATIO-- 2 C r B c I IN V E N TOR W L. BRUNE JZMVALV W ATTORNEV April 27, 1954 w. L. BRUNE TRANSMISSION MEASURING MEANS ANDMETHOD Filed Sept. 30, 1952 '7 Sheets-Sheet 3 R. m w m 2 MW EN 0 0 G G NN n m u 0 mm PC E M R N 5 05 R 2 MR fi amm m/ m s 1 MM M M 5 mm C0 0 M Rw 6 NC 0 TD W W swim wwr MW 0 A u a G G F F lNl/ENTO/P W L. BRUNEATTORNEY April 27, 1954 w. BRUNE TRANSMISSION MEASURING MEANS AND METHODFiled Sept. 30, 1952 7 Sheets-Sheet 4 w A D m w R M A m FIG. /5

TRANSFER ADMITTANCE= //vv/v roe W L. BRUNE ATTORNEY 7 Sheets-Sheet 5 W.L. BRU N E APPARATUS UNDER TEST TRANSMISSION MEASURING MEANS AND METHODFiled Sept. 30, 1952 April 27, 1954 ATTORNEY INVENTOR W L. BRUNE WWW VVY

April 27, 1954 w. L. BRUNE 2,677,101 TRANSMISSION MEASURING MEANS ANDMETHOD Filed Sept. 50, 1952 7 Sheets-Sheet 6 T0 SECOND DETECTOR T0 FIRSTDETECTOR To GENERATOR FIG. 24

INVENTOR n L. BRUNE ATTORNEY April 27, 1954 w. L. BRUNE 2,677,101

TRANSMISSION MEASURING MEANS AND METHOD Filed Sept. 30, 1952 7Sheets-Sheet 7 M/l EA/TOR By W L. BRUNE GWM A 77'ORNE Y Patented Apr.27, 1954 TRANSMISSION MEASURING lVIEAN S AND METHOD William L. Bruno,Florham Park, N. 3., assignor to Bell Telephone Laboratories,Incorporated, New York, N. Y., a corporation of New York ApplicationSeptember 30, 1952, Serial No. 312,313

11 Claims.

This invention relates to measuring systems for electrical networks andmore particularly to systems for measuring frequently used transmissionratios such as are commonly designated voltage ratios, current ratios,transfer impedances and transfer admittances.

Voltage ratio, current ratio, transfer impedance, and transferadmittance are used singly or together to indicate the performance to beexpected of an electrical network upon insertion in a system with otherelectromagnetic elements. A general object of the invention is tomeasure one or more of the above-mentioned ratios for any given networkwith an accuracy which is not impaired by additional or stray impedancesintroduced into the measuring system by the measuring apparatus.

A more specific object of the invention is to eliminate as much aspossible the effect of the generator and detector impedances upon theaccuracy of the measurements.

Another object is to avoid impairment of the accuracy of themeasurements by the presence of common ground connections to differentpieces of measuring equipment involved in the measurements.

In the drawings:

Figs. 1 1 are circuit diagrams relating to a simple arrangement formeasuring voltage ratio;

Fig. 5 is a diagram showing an ideal measuring condition for voltageratio;

Figs. 6-9 are schematic circuit diagrams of an improved system for thepractical measurement of voltage ratios;

Fig. 10 is a diagram showing an ideal measuring condition for currentratio;

Figs. 1144 are schematic circuit diagrams of a practical system formeasurement of current ratios;

Fig. is a diagram showing an ideal measuring condition for transferimpedance;

Figs. 16 and 17 are schematic circuit diagrams of a practical system formeasurement of transfer impedance;

Fig. 18 is a diagram showing an ideal measu ing condition for transferadmittance;

Figs. 19 and 20 are schematic circuit diagrams of a practical system formeasurement of transfer admittance;

Fig. 21 is a diagram illustrating how measuring methods for use upon athree-terminal network may be extended to networks of any number ofterminals;

Figs. 22 and 23 are schematic circuit diagrams of a particular systemfor testing transformers;

Fig. 24 is a plan view, partly broken away, showing a testing fixture orjig and a transformer placed in the jig for testing, together withconnecting cords and plugs used in testing;

Fig. 25 is an elevational View, partly broken 2 away, showing thetesting jig and transformer without the connecting cords and plugs ofFig. 24; and

Fig. 26 is a perspective view of the aforesaid transformer standingalone.

In 1, a generator I of electromotive force e and internal impedance Z1is shown connected to apparatus 2 which it is desired to test. Theapparatus 2 is represented schematically as a conventional transmissiondevice with an input side connected to a pair of terminals 3 and i andan output side connected to a pair of terminals 5 and t.

An illustrative use of the testing system and method in accordance withthe invention is to determine the ratio between the generator voltage eand the open circuit voltage V at the terminals 5 and 8. The impedancelooking toward the generator I from the terminals 5 and 6, is designatedZ3 and together with the open circuit voltage V is indicated inconventional manner in Fig. l. The ratio which it is desired todetermine is No detector is known that can directly and accuratelymeasure the voltage V because the detector will have an impedance,herein designated Z2, which cannot be infinitely great and hence cannotconstitute a completely open circuit termination for the apparatus 2under test.

To nullify the eiiect of the lack of infinite greatness of the detectorimpedance, Z2, voltage measurements are made with two different circuitconnections, namely as shown in Figs. 2 and 4 respectively from whichmeasurements the desired transmission ratio is determinable.

Fig. 2 shows the generator I and apparatus 2 under test, connected to adetector l of impedance Z2 as hereinabove specified, through a passiveimpedance element 3 of the same impedance value Z1 as the generator I,the impedances Z1, Z2 and Z3 being serially connected. From wellknowncircuit theory, the voltage V1 across the detector terminals shown at 12and I3 is given y 3 wherein the passive impedance element 8 is connectedacross between the terminals 3 and 4.

In Fig. 3, the impedance looking back from the terminals and 6 towardthe apparatus 2 and element a has the value Z3, the same as theimpedance Z3 in Fig. 1. It is evident that all the same circuitimpedance values are present in Fig. 3 as in Fig. 1 and that they havethe same circuit configuration in both figures, only the generatedelectromotive force having been changed, in this case, reduced from c tozero. The voltage across between the terminals 5 and 6 on open circuit,as represented in Fig. 3 is therefore zero. The element 8 provides acompensatory terminating arrangement at the input side of the network 2,taking the place in the second circuit connection, Fig. 4, of thegenerator I in the first circuit connection, Fig. 2.

In Fig. 4 the circuit elements of Fig. 3 are shown connected to thedetector 1 through the oscillator I to form the second circuitconnection above mentioned, wherein conventional circuit theory showsthat the voltage V2 across the detector terminals I2 and I3 is given byZ2 "z1+z2+z3 The ratio n1 V2 6 thus comes out to be the ratio desired,and the result is independent of the particular values of Z1, Z2 and Z3.

The arrangement and method described in connection with Figs. 1-4, whilesimple and straightforward and involving but two readings of a singledetector, require complete isolation of the generator i and detector 1.If the generator and detector have in fact a common ground connection,thepassive element 8 will be short-circuited by the common groundconnection in the circuit of Fig. 2, whereas in the circuit of Fig. 4the common ground connection will have no corresponding short-circuitingeffect. Accordingly, the accuracy of the determination of the voltageratio is seriously impaired by the common ground connection. It willalso be noted that the measured value of the voltage ratio applies notto the network 2 alone but to the network 2 plus the impedance Z1connected between the terminals 3 and it, since e is the voltage appliedbetween the network 2 and the impedance Z1 and not directly between theterminals 3 and 4.

An ideal measuring circuit for voltage ratio is shown in Fig. 5 in whicha three-terminal network Hi2 has an electromotive force e impressedacross its input terminals and a voltage V is measured across its outputterminals. Neither e nor V involves any extraneous impedance. Thenetwork is shown as a conventional T-network with input series arm A,output series arm B, and shunt arm C. The side of the network betweenthe external terminals of the arms A and C is designated herein as theinput side of the network and the side between the external terminals ofthe arms B and C is designated as the output side. This designationrelates to the direction in which transmission through the network isdesigned to take place and the same network may be used for transmissionin the opposite direction when desired, in which case the input andoutput sides may be redesignated accordingly. The values of voltageratio and current ratio of any network, of course, are differentdepending upon the direction of transmission, except in the case of asymmetrical network that is where A and B are equal.

To obviate inherent difficulties of the system of Figs. 1-4 and toclosely approximate ideal measuring conditions, various arrangementsinvolving two readings each of two detectors may be used for determiningthe voltage ratio of a network to be tested, or to determine the currentratio, transfer impedance, or transfer admittance of the network. Onepair of readings is obtained with the elements of the measuring systemarranged in a first circuit connection and the other pair of readings isobtained with the circuit elements rearranged in a second circuitconnection, similarly to the manner in which a first reading of thesingle detector in Figs. 2 and 4 is obtained in the first circuitconnection shown in Fig. 2 and a second reading of the detector isobtained in the second circuit connection shown in Fig. 4.

Voltage ratio An arrangement specifically for measuring voltage ratiosto closely approximate the ideal value defined by the circuit of Fig. 5is shown in Figs. 6-9. The reference numeral Hi represents a combinationof the generator of electromotive force e and internal impedance Z1connected in parallel with a first detector D1 of internal impedance Z2.The detector D1 is, for the purpose of measuring the voltage ratioalways connected across the generator and measures the voltage acrossany pair of circuit points between which the combination is connected.In the first circuit connection, Figs. 6 and '7, the combination I4 isconnected between the input terminals of the apparatus 32 to be tested,the latter being represented in Fig. 7 by the T network as in Fig. 5.The second detector I5 is connected across the output side or thenetwork :92. In the second circuit connection, Figs. 8 and 9, thecombination It is removed from the input terminals of the network 2,replaced by a short circuit lead 200, and inserted instead in the lead2M from the external terminal of the shunt arm C to the second detectorIt. .This short circuit lead 200 constitutes a compensatory circuitterminating arrangement at the input side of the network, taking theplace of the combination Hi. By the same token, the lead 284 constitutesa compensatory circuit terminating arrangement at the output side of thenetwork, taking the place in Fig. '7 of the network I 4.

In the operation of the system of Figs. 6-9 to determine the voltageratio of the apparatus M2, the currents i1 and is indicated by therespective first and second detectors, or the ratio of these currents,may be read with the circuit configuration as in Fig. '7 and thecurrents is and is or their ratio may be read with the circuitconfiguration as in Fig. 9. The voltage ratio is given by aiS A+C whichrelationship may readily be verified by solving the circuits of Figs. 7and 9 by wellknown algebraic methods. It will be noted that the actualcurrents ii, i3, i5 and is need not be measured, it being sufiicientthat the two ratios ii/i3 and iii/2'5 are each determined. Switchingbetween the respective circuit connections of Fig. 7 and Fig. 9 may beeffected readily in accordance with well-known techniques such as thoseemploying jacks and plugs together with flexible connectors, cords orshort transmission lines.

The compensatory nature of the circuit terinating arrangement comprisingthe short circuit lead 29!) across the input side of the network=voltage ratio in the second circuit connection Fig. 9, and lead ZUI atthe output side in the first circuit connection, Fig. 7, are such as tohelp bring about Current ratio An ideal measuring condition fordetermining the current ratio of a three-terminal network is shownschematically in Fig. 10, it being assumed thatthere are no extraneousimpedances introduced into the circuit in connection with themeasurement of either the input current I1 or the output current I2.

Circuit connections for closely approximating the ideal condition ofFig. are shown in block form in Figs. 11 and 13 and by equivalentcircuit diagrams in Figs. 12 and 14. Fig. 11 shows a series combinationit of the generator and first detector connected across the inputterminals of the network 152 to be tested. The second detector I5 is inthis case not connected directly across the output terminals of thenetwork I82, but instead a shielded repeating coil or transformer I!having separate shields for the two windings is inserted between thenetwork 2 and the detector 15. The requirement for coil I! is that thesecondary current shall be a function of the primary current alone.There may be a stray impedance path, such as a capacitance, between theshields oi" the respective primary and secondary windings, the value andcircuit location of which is shown in Figs. 12 and 14 by an impedanceelement designated Z5. Due to the common ground connections of themeasuring devices l5 and it, the impedance Z5 is effectively coupledinto the measuring systems as shown in Figs. 12 and 14. The impedancelooking into the primary winding of the coil I! is assumed to be theimpedance Z4 oi the second detector multiplied by a frequency variablefactor a' characteristic of the coil i? and the secondary current of thecoil is assumed to be equal to the primary current multiplied by afrequency variable factor it, in accordance with the requirement of coilI! given above. The coil i7 serves to prevent the short circuiting ofthe generator by the common ground connection, in Figs. 12, 14, 16 and20.

The detector D1 is in this case always connected in series with thegenerator and measures the current delivered by the generator into anycircuit branch into which the combination is inserted. As shown in Fig.12, the combination I6 is connected between the input terminals of theapparatus I32 to be tested.

In the second circuit connection, Figs. 13 and 14, the combination it isconnected in parallel with the output terminals of the apparatus I02 andthe input terminals of the apparatus l02'are left on open circuit.Conversely, in the first circuit connection, Figs. 11 and 12, thecombination [6 is connected in parallel with the input terminals of theapparatus 102 and the position of combination IS in the second circuitconnection is left open-circuited. In these cases an open circuit is thecircuit terminating arrangement which properly compensates for thecombination i6, as is borne out by calculations.

In the operation of the system of Figs. 11-14 to determine thetransmission current ratio of the apparatus I92, the ratio of thecurrents i7 and kis is measured in the circuit of Fig. 12 and the ratioof the currents (ho-1'11) and Iain is measured in the circuit of Fig.14. The transmission current ratio is given by fi 1 5 current ratiowhich relationship is readily verifiable by algebraic solution of thecircuits of Figs. 12 and 14. It will be noted that the value of thestray impedance Z5 cancels out of the calculations and hence does notarfect the accuracy of the measurement of the current ratio.

Transfer impedance An ideal measuring condition for determining thetransfer impedance oi a three-terminal network is shown schematically inFig. 15, it being assumed that there are no extraneous impedancesintroduced into the circuit in connection with the measurement either ofthe output voltage V or of the input current 11.

Circuit connections for closely approximating the ideal value defined byFig. 15 are shown by circuit diagrams of Figs. 16 and 17. In Fig. 16 theseries combination 16 of generator and first detector is connectedacross the input terminals of the network to be tested. The repeatingcoil I! is inserted between the output terminals of the network and thesecond detector. The common ground connection between a point incombination I6 and a point in detector it results in a coupling of thestray impedance Z5 into the measuring circuit. In Fig. 17, as comparedto Fig. 16, the series combination it of generator and first detectorhas been removed from the input of the network, leaving the latteropencirouited at the input side and the parallel combination I 4 ofgenerator and first detector has been inserted between the externalterminal of the shunt arm of the network IE2 and the repeating coll. Inthis case-the stray impedance Z5 is short-circuited by the common groundconnection and accordingly is not coupled into the measuring circuit.The effect of the impedance Z5 cancels out in taking the ratio of thedetector currents in the circuit of Fig. 16 and hence does aifect theaccuracy of the measurement of transfer impedance.

In the operation of the system of Figs. 16-1 to determine the transferimpedance of the apparatus under test, the ratio or" the currents in andkit; is measured in the circuit of l8 and the ratio of the currents inand kz'is is measured in the circuit of 17. The transfer admittance isgiven by @M=C=negative of transfer impedance it being necessary in thiscase, in order to determine the value of the transfer impedanceabsolutely, that the value of the impedance of the first detector beknown. The value Z4 of the impedance of the second detector cancels outof the calculations and need not be known. The negative sign is ofimportance when the phase as well as the amplitude of the transferimpedance'i's to be determined.

Transfer admittance An ideal measuring condition for determining thetransfer admittance of a three-terminal network is shown schematicallyin Fig. 18, there being no extraneous impedances introduced into thecircuit in connection with the measurement either of the output currentI2 or of the input electromotive force e.

Circuit connections for realizing the accurate measurement of thetransfer admittance defined by Fig. 18 are shown in Figs. 19 and 20. InFig. 19 the parallel combination of generator and first detector isconnected across the input terminals of the network to be tested. Therepeating coil H is inserted between the output terminals of the networkand the second detector. As is seen from Fig. 19, the stray impedance Zis not coupled into the measuring circuit despite the common groundconnections of the measuring units. In Fig. 20 as compared to Fig. 19,the parallel combination of generator and first detector has beenreplaced by a short circuit and a series combination of generator andfirst detector has been shunted across the output terminals of thenetwork under test. The stray impedance Z5 is coupled into the measuringcircuitby the common ground connections of the measuring units, but thevalue of Z5 cancels out in taking the ratio of the currents in the firstand second detectors.

In the operation of the system of Figs. 19-20 to determine the transferadmittance of the apparatus under test, the ratio of the currents(ire-4'19) and kiao is measured in the circuit of Fig. 19 and the ratioof the currents (in-42s) and kin is measured in the circuit of Fig. 20.The transfer admittance is given by =transfer admittance General Uponmeasuring and taking into account in known manner the phase differencesbetween the respective detector currents and their effect upon thecurrent ratios in the measuring circuits the systems illustrated willyield values of complex voltage ratios, complex current ratios, andcomplex transfer impedances and admittanoes. In other words, eachdetector may be arranged to measure not only the amplitude but also thephase of the current passing therethrough and from such measurements thephase shift of a net work to be tested may be ascertained in addition toits amplitude transmission characteristics. 7

While the measuring methods illustrated have been shown as applied to athree-terminal network, corresponding measurements may be made onnetworks with more than three accessible terminals by repeatedapplication of the same procedure. lustrated at 262 in Fig. 21 witheight terminals ll through 48, by way of example. The input may beimpressed upon any two terminals, such as H and 42, of which terminal Mfor example, may be grounded as shown in Fig. .21, and

The apparatus under test may be as il- 7 the output voltage may bemeasured between the grounded terminal 4! and any one of the remainingterminals 43 through 58, for example, voltage V1 at terminal 46 aillustrated in the figure. If it is desired to measure the outputbetween any two non-grounded terminals, for example, between 45 and 46,two complete sets of measurements are made, one set being for the outputmeasured between terminals 41 and 45, and the other set being for theoutput measured between terminals t] and 4B. The difference between theresults of the two sets of measurements gives the voltage betweenterminals 45 and Q6. As noted in Fig. 21, if V1 is the voltage measuredbetween terminals 46 and il and if V2 is the voltage measured betweenterminals 45 and M, then the voltage V3 between terminal 46 and terminal4-5 is given by V3=V2V1. Similarly, current ratios, transfer impedancesand transfer admittances between any two non-grounded terminals may bedetermined by repeated applications of the methods hereinbeforedescribed.

Inspection testing of component parts of transmission systems A furtherillustrative use of the invention is in connection with the measurementof the voltage ratio of manufactured component parts such as two-windingshielded transformers for service in a coaxial cable transmissionsystem. Figs. 22 and 23 respectively represent schematically twosuitable measuring conditions for use with such a transformer. In thesefigures, the transformer is shown at 50 and has windings 5|, 52, 53,with a shield surrounding the winding 53 and connected to the lower endof Winding 53. The transformer has another shield 56 between thewindings El, 52 and the winding 53, which shield is not connectedintentionally to any of the wind ings. Stray impedances 57 and 58effectively connect any point of winding 5! or 52 respectively to thelower end of winding 53. Input termination simulating resistors 59, 60may be provided if desired, to simulate actual transmission lineconditions at the input side of the transformer 50 in service. Aresistor 6| may be provided in the output circuit of the transformer forthe express purpose of coupling the output circuit to the strayimpedance meshes containing the impedances 5'! and 58 so that thepresence of impedances 5'! and 58 will affect the measurements. Ifimpedances 51 and 58 are abnormally low in a given sample of transformerbeing tested, the fact will be made evident by a measured value ofvoltage ratio that is inconsistent with the usual value of voltage ratiofor a satisfactory transformer. Without a coupling impedance in theposition of resistor 6!, the impedances 5i and 58 might not appreciablyaffect the voltage ratio measurement. The presence of the resistor 8!does not appreciably affect the simulation of an open circuit conditionin the output circuit of the transformer 50 as the resistance of theelement 61 is effectively in series with an infinitely large impedance.

In making a voltage ratio determination, one circuit condition is asshown in Fig. 22. Here, a parallel combination of a generator of voltagee and a first detector D1 is inserted between resisters 59 and, Gil. Asecond detector D2 is connected between terminal 15 (of transformer 50)and terminal 63. The generator and the two detectors are each assumed tobe grounded. It is arranged that the grounded points of the generatorand detector D are connected together and directly connected to terminal62 of the resistor 59 on the side of the resistor away from the windingill. The ground point of the detector D2 is connected to terminal 63 onthe side of the resistor El away from the winding 53. A bus 54 connectsthe shield 56 to the terminals 62 and 33 while the transformer 5c isunder test. With the circuit as shown in Fig. 22 a first comparison ismade of the readings of the detectors D1 and D2.

The other circuit condition is as shown in Fig. 23, where a shortcircuit is substituted for the combination of generator and detector D1between resistors 59 and Gil. This generator-detector combination isinserted instead between the terminal 63 and the grounded side ofdetector D2, with the grounded terminals of the generator and detectorD1 directly connected to the grounded side of detector D2. As in thecircuit of Fig. 22, the bus 5 connects the terminals 62 and 63 duringthe test although in th circuit of Fig. 23, the terminals 52 and 63 areno longer grounded. With the circuit as shown in Fig. 23 a secondcomparison is made of the readings of the detectors D1 and D2. Furthercomparison of the results of the respective measurements with thecircuits of Figs. 22 and 23 yields the desired value of the voltageratio of the transformer at as if the transformer were working into anopen circuit.

A fixture or jig for facilitating rapid testing of substantiallyidentical transformers or other circuit elements is shown in Figs. 24and 25. This jig is arranged to give the circuit configuration of eitherFig. 22 or Fig. 23 and to change from one of these configurations to theother merely by interchanging a special plug from one receptacle toanother.

A transformer for which the jig is designed is shown by itself in Fig.26. The transformer has accessible terminals I through 15, which areshown schematically in Fig. 23 corresponding to the pictorialrepresentation of the same terminals in Fig. 26. Terminal 1c isconnected tothe shield 56. Terminal ll is connected to the lower end ofwinding 5!, terminal 12 to the common terminal of windings 5i and 52,terminal 13 to the upper end of winding '52, terminal M to the lower endof winding 53 and to the shield 54, and terminal is connected to theupper end of winding The resistors 59, 5 3 and Si are built into thetesting jig and are identified in Figs. 2c and 25 by the same respectivereference numerals in the schematic diagrams of Figs. 22 and 23.

Fig. 24 shows the measuring condition of Fig. 22, in which a plug 83! isplugged into a conductive receptacle ill, a conductive tip 82 of theplug making contact with an insulated flexible contactor 83 andseparating said contactor from a fixed contactor 8:; which latter isconductively connected to the receptacle 8% and is identified with theterminal 32 of Fig. 22. The plug 8!! terminates fiexible coaxial cables85 and 86 which are for connection respectively to the generator and thefirst detector D1. The sheaths of the cables 85 and at are connectedtogether and to the sheath of the plug St so that when the plug 8d is inthe receptacle 8i the sheaths are connected to the contact 34. Thecentral conductors of the cables 85 and 86 are both connected to the tip32 so that when the plug is in the receptacle the non-grounded terminalsof the generator and the first detector are connected to the flexiblecontactor 83 and the generator and first detector are inserted in thecircuit as shown schematically in Fig. 22. The sheath of the plug andthe tip 82 are insulated from each other within the plug 80.

A connection from the second detector D2 is provided in a flexiblecoaxial cable 8? which is shown plugged into a receptacle 88 which ispart of a shielded probe amplifier 89. The input of the probe amplifierhas one terminal connected to the terminal it of the transformer 86 andthe other terminal connected to a fixed contactor 99 associated with aflexible contactor 9! in a receptacle 92 substantially identical to thereceptacle iii. The flexible contactor 9! is connected to the end of theresistor (it away from the terminal i l of the transformer 56. Thesheath of cable 81 goes to the grounded side of the second detector.

A conductiv framework 93, provided with a removable conductive shieldingcover 9 serves as the bus 54 of Fig. 22 and interconnects the fixedcontactor 8d of receptacle 8!, a spring contactor Ii! which contacts thetransformer shield terminal l9, and the flexible contactor SI of receptacle 9E. The probe amplifier is insulated from the bus 64 by aceramic insulator 96. Power is supplied to the probe amplifier by apower cable 9! with appropriate fittings.

In addition to the spring contactor Hi3 contacting terminal it oftransformer 55 when the transformer is in place in the jig, other springcontactors H I, H 3, H4 and H5 contact terminals ii, 73, 7d, and 2'5,respectively. Within the jig, the contactors llii, HI, H3, H4 and H5,

' respectively are connected to the body or" receptacle 8|, resistor 59,resistor 69, resistor El, and to a shielded slidable input lead H5projecting from the probe amplifier 89. The contactors Ht, HI, H4 aremounted on an insulating arch shaped member ill and the contactor H3 ismounted on an arcuat insulator H8. Contactor H5 is attached to probe H6.

The transformer 5d slides into the jig on ways H9, I20 to a positionunder the insulators H1 and I it in which the contactors engage thetransformer terminals and is held in place by a light spring latch 52!.Shielded input lead H5 is then advanced until contact H5 engagesterminal '55. A flexibl contactor E22 serves to connect the core of thetransformer 59 to the framework 93 during the test. A transformer may beremoved from the jig and another substituted with a minimum of time andefiort.

For the second measuring condition, corresponding to the circuit of Fig.23, the plug 86] is merely removed from the receptacle 8! and insertedin the receptacle 52. This operation transfers the generator and firstdetector as required to convert the circuit of Fig. 22 into the circuitof Fig. 23. This involves closing contact between flexible contactor 83and fixed contactor in receptacle 8! and breaking contact betweenflexible contactor 9! and fixed contactor 9b in receptacle 92, as wellas transferring tip 82 from contactor 83 to contactor 9i.

Readings are taken on detectors D1 and D2 in each of the two circuitconditions and from these readings the effective voltage ratio of thetrans- .former Si) is readily found in accordance with the methoddescribed hereinabove in connec tion with Figs. 22 and 23, as well as inconnection with Figs. 7 and 9.

It is to be understood that the above-described arrangements areillustrative of the application of the principles of the invention.Numerous 1 1 other arrangements may be devised by those skilled in theart without departing from the spirit and scope of the invention.

What is claimed is:

1. A system for measuring transmission ratios, comprising a source ofelectromotive force, a detector, a network to be tested having an inputside and an output side, said system making use of first and secondcircuit connections for measuring a single transmission ratio, in thefirst of which connections the source of electromotive force isconnected to the input side of the network and a compensatory circuitarrangement is provided on the output side of the network, and in thesecond said circuit connection the source of electromotive force isconnected to the output side of the network and a compensatory circuitarrangement is provided on the input side of the network, said detectorbeing connected to the output side of the network in both the first andthe second circuit connection.

2. A system for measuring transmission ratios, comprising-a source ofelectromotive force, a first detector directly coupled to said source, anet-- work to be tested having an input side and an output side, saidsystem making use of first and second circuit connections to supplyindications to be combined to measure a single transmission ratio of thenetwork to be tested, and a second detector connected to the output sideof the network in both the first and second circuit connection, saidsource and first detector in the first circuit connection beingconnected to the input side of the network and in the second circuitconnection being connected to the output side of the network, acompensatory network arrangement being provided on the output side ofthe network in the first circuit connection and on the input side of thenetwork in the second circuit connection.

3. A system in accordance with claim 2, in which the source and thefirst detector are connected directly in parallel with each other inboth the first and the second circuit connection,

and in which each said compensatory network arrangement is a shortcircuit.

4. A system in accordance with claim 2, in which the source and thefirst detector are connected directly in series with each other in boththe first and the second circuit connection, and

in which each said compensatory network arrangement is an open circuit.

5. A system in accordance with claim 2, in which in the first circuitconnection the source and the first detector are connected directly inseries with each other and in the second circuit connection areconnected directly in parallel with each other, and in which thecompensatory network arrangement provided on the output side of thenetwork m the first circuit connection is a side of the network and theother such point being short circuit and the compensatory networkarrangement provided on the input side of the ne work in the secondcircuit connection is an open circuit.

6. A system in accordance with claim 2, in which in the first circuitconnection the source and the first detector are connected directly inparallel with each other and in the second circuit connection areconnected directly in series with each other, and in which thecompensatory network arrangement provided on the output side of thenetwork in the first circuit connection is an open circuit and thecompensatory network arrangement provided on the input side of thenetwork in the second circuit connection is a short circuit.

'7. A system for measuring transmission ratios, comprising a source ofelectromotive force and an associated first detector, a network to betested having an input side and an output side, a second detectorconnected to the output side of the network, and means to connect saidsource and associated first detector to the input side of the networkfor a first comparison-of readings of the two detectors, means totransfer the said source and. first detector to the output side of thenetwork for a second comparison of readings of the two detectors.

8. A system for measuring the voltage ratio of a network having an inputside and an output side, comprising a source of electromotive force, afirst detector connected directly in parallel across the terminals ofsaid source, said system making use of first and second circuitconnections to supply indications to be combined to measure said ratio,and a second detector connected to the output side of the network inboth the first and the second circuit connection, said parallelcombination of source and first detector being connected to the inputside of the network in the first circuit connection and to the outputside of the network in series with the second detector in the secondcircuit connection, and the input side of the network being terminatedin a short circuit in the second circuit connection.

9. A method of measuring a transmission ratio of a given three-terminalnetwork having designated input, and output sides which method comprisesimpressing an electromotive force upon the input side of the network,measuring the ratio between an input current and an output current,removing said electromotive force from the input side of the network,impressing an electromotive force upon the output side of the network,and measuring the ratio of a current at the point of application of thelast-mentioned electromotive force to an output current at the samepoint as in the previous measurement.

10. A method of measuring a transmission ratio of a given three-terminalnetwork which comprises impressing an electromotive force upon the inputside of the network, measuring a ratio of an input current and an outputcurrent of said network, removing said electromotive force from theinput side of the network, impressing an electromotive force upon theoutput side of the network, and measuring a ratio of currents in twodifferent portions of the output side of the network.

11. lhe method of measuring a transmission ratio of a network havingdesignated input and output sides which method comprises energizing thenetwork from one side, measuring the ratio of currents at two points inthe system outside the network, one such point being on the output onthe side from which the network is energized, energizing the networkfrom the other side, measuring the ratio of currents at two pointsoutside the network, one such point being the same point on thedesignated output side of the network as before and the other such pointbeing on the side from which the network is energized.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,518,543 Nyquist Dec. 9, 1924 1,725,756 Gannett Aug. 27, 19292,129,880 Scherbatskoy et a1. Sept. 13, 1938

